Paving machines are used for depositing, spreading, compacting, and smoothing paving material on a roadbed in such a manner that a uniform and drivable surface is produced. Screed assemblies are used to smooth and compact the paving material. The screed assembly is typically drawn behind the paving machine and is adjustable to establish both the thickness of the deposited layer of paving material and the width of the area over which the material is spread.
Modern screed assemblies typically include one or more base or fixed portions and one or more extendable portions that may be adjusted relative to the fixed portions to control the working width of the screed assembly. A common arrangement uses two base portions arranged end to end such that they may be independently tipped from horizontal to permit laying a paved mat having a desired cross-section, for example, a center crown. Each base portion commonly includes an extendable portion that may be moved inwardly to minimize the width of the screed assembly during transport and may be extended outwardly up to a maximum extension length to increase the paving capacity of the machine.
It is desirable to provide a screed assembly in which the fully extended screed width is at least twice the fully retracted width. However, achieving a full doubling of screed width is difficult because of necessary structural overlaps in portions of the fixed and extendable screed elements. Because of this, the fully extended screed width is typically several centimeters less than double the fully retracted width.
One example of a screed assembly adapted to address this problem is found in U.S. Pat. No. 4,986,695, which describes an apparatus that uses a number of telescopic rods to permit elongation of the base screed portion in the extended position. However, this is a complex mechanical arrangement involving multiple components moving relative one to the other, and may not be suitable for screed assemblies where a high degree of rigidity is required and where simplicity of operation is necessary for trouble-free operation.
The present invention is directed to providing a double extending screed that overcomes one or more of the problems set forth above.